Heating apparatus and process

ABSTRACT

Furnace apparatus and process for heating a fluid. The furnace has an elongated heating chamber, a fluid conveying conduit which extends axially through the chamber, furnace burners and means to control the temperature profile and heat energy in the furnace. The heating chamber is provided with a flue gas outlet adjacent the conduit outlet. In operation, the furnace is fired differentially with the heaviest firing at the conduit inlet. The hot combustion gases from the burners flow parallel and cocurrently with the fluid in the conduit and discharge from the furnace at the flue gas opening.

United States Patent Dutkiewicz [451 July 18,1972

[54] HEATING APPARATUS AND PROCESS [72] Inventor: Bronislaw K. Dutkiewicz, New York, NY.

[73] Assignee: Stone & Webster Engineering Corporation, Boston, Mass.

[22] Filed: Jan. 19, 1970 [21] Appl. No.: 3,832

[52] US. Cl. ..122/240 A, 122/333, 122/356 [51] Int.Cl ..F22b31/00 [58] FieldofSearch ..l22/333,240,356

[56] References Cited UNITED STATES PATENTS 2,292,682 8/1942 Barnes ..122/356 2,634,712 4/1953 Kallam ..122/356 3,230,052 l/1966 Lee et al. ..122/356 X 3,348,923 10/1967 Demarest ..122/346X 3,469,946 9/1969 Primary Examiner-Kenneth W. Sprague Attomey-Morgan, Finnegan, Durham & Pine [57] ABSTRACT Furnace apparatus'and process for heating a fluid. The furnace has an elongated heating chamber, a fluid conveying conduit which extends axially through the chamber, furnace burners and means to control the temperature profile and heat energy in the furnace. The heating chamber is provided with a flue gas outlet adjacent the conduit outlet. In operation, the furnace is fired differentially with the heaviest firing at the conduit inlet. The hot combustion gases from the burners flow parallel and cocurrently with the fluid in the conduit and discharge from the furnace at the flue gas opening.

8 Clains, 7 Drawing Figures Wiesenthal ..122/3$6 X Y Patented July 18, 1972 3,677,234

4 Sheets-Sheet l I4 I A 2L5" Wm, H U f FIG. I

INVENTOR. BRONISIAW l1. DUTKIE' W/CZ A 7' TOR/V575 Patented July 18, 1972 3,677,234

4 Sheets-Sheet 2 FIGS ' 'j Z4 INVENTOR.

BRlM/ISLAW K DUTIf/EWICZ Patented July 18, 1972 4 Sheets-Sheet 5 F IG. 4

70 INVENTOR.

BROIV/SZAW M HUT/17E W/CZ Arroeus r HEATING APPARATUS AND PROCESS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to furnace apparatus and a method for heating fluid material as it passes through the furnace. More particularly, the invention relates to furnace apparatus and a process for carrying out hydrocarbon conversion processes which comprise heating hydrocarbon feed to a high temperature and maintaining it at a high temperature for a short reaction time.

The furnace and process of the present invention is particularly suitable for carrying out hydrocarbon pyrolysis under conditions of short residence time, high temperature and low hydrocarbon partial pressure to achieve high selectivity to olefin production, particularly ethylene, and high ratios of olefin yield to saturates such as methane, ethane, propane, etc.

2. Description of the Prior Art Presently, the state of the furnace art includes furnaces for heating fluid in tubes which are designed to achieve control of the temperature of the tubes.

Furnaces are known which include means for providing heat energy at the localized areas. However, the present state of the art does not include the combination of a furnace design which facilitates maximum use of the total heat energy introduced into the furnace and control of a temperature profile over the furnace conduit.

Basically, control of the temperature profile of a furnace conduit through which fluid is passing has in the past been achieved by providing a furnace with a plurality of variable burners located at various localized areas. Torch type flame burners and radiant burners have both been used to provide a variable amount of heat energy to a localized area on the furnace conduit. Illustrative of the apparatus used to achieve a regulated temperature profile are the furnace designs disclosed in U.S. Pat. No. 2,638,879 (May 19, 1953) issued to Hess and U.S. Pat. No. 3,062,197 (Nov. 6, 1960) issued to Fleischer.

However, until the present invention, the hot combustion gases emanating from the burners have usually been exhausted from the furnace after performing the primary function of heating a localized area of the conduit.

SUMMARY OF THE INVENTION Objects of this invention include the provision of a novel configuration of a furnace and conduit distribution which affords increased furnace efficiency and lower conduit temperatures or increased processing capacity of the furnace as compared to a conventional single firebox furnace of the type now in common use.

It is a particular object of the present invention to provide a furnace which will facilitate heating the entire conduit or conduits through which the fluid to be heated flows to the maximum tube metal temperature.

It is a further object of the present invention to provide a furnace which transfers a maximum amount of heat to the fluid passing through the furnace conduit or conduits at the fluid inlet section.

A still further object of the present invention is to provide a furnace which uses the heat energy from the furnace burners to heat the fluid in the furnace conduits initially in the area of the conduit inlet and subsequently in the area downstream of the inlet.

Another object of the present invention is to provide a furnace wherein the hot gas combustion products emanating from the furnace burners pass parallel and co-currently with the fluid being heated in the furnace conduit or conduits.

It is also an object of the present invention to provide a furnace in which the temperature profile of the furnace conduit or conduits can be controlled.

With the novel furnace configuration and conduit distribution, it is also possible to provide increased furnace efficiency and lower conduit temperatures while at the same time increasing the processing capacity of the furnace. Attainment of these objects results in decreasing the cost of the furnace and improving the flexibility of operation and temperature profile control.

The furnace of the present invention comprises a wall structure of refractory material which defines an elongated chamber. A conduit or conduits, such as metal tubes, for carrying fluid to be heated, extend from'one end of the chamber to the other. The conduit is substantially parallel to the axis of the chamber from one end thereof to the other. Such parallel relationship excludes serpentine or turns, unless the chamber itself has a corresponding turn in the vicinity of the conduit. Burners, which can be of the radiant heating type, or of both the radiant heating and long flame heating type, are provided in the furnace. The burners are provided with means, such as valves, to regulate the amount of heat energy emitted therefrom. A flue gas outlet with draft control means is provided at the outlet end of the chamber adjacent the conduit outlet for the passage therethrough of the hot burner combustion gases.

In operation, fluid, e.g., hydrocarbon, flows through the conduit from the inlet end of the chamber to the outlet end of the chamber. Similarly, the hot combustion gases from the burners flow from the inlet end of the chamber to the outlet end of the chamber and ultimately through the flue gas outlet located in proximity to the conduit discharge end. Consequently, in the downstream section and preferably throughout the entire chamber, the hot combustion gases flow parallel and cocurrently with the fluid in the conduit.

DESCRIPTION OF THE DRAWINGS The invention will be better understood when considered in conjunction with the accompanying drawings wherein:

FIG. 1 is a cross-sectional plan view of a furnace embodying the invention;

FIG. 2 is a vertical cross-sectional view taken on the line 2- 2 of FIG. 1;

FIG. 3 is a partially cut away side elevation of a preferred embodiment of this invention;

FIG. 4 is a cross-sectional front elevational view of the furnace of FIG. 3;

FIG. 5 is a cross-sectional plan view of the furnace of FIG. 4 taken on the line 5-5.

FIG. 6 is a graphical representation of temperature profiles for a conventional single firebox furnace of the type in common use today; and

FIG. 7 is a graphical representation of temperature profiles for a furnace of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiment of the furnace of the present invention depicted in FIGS. 1 and 2 is a single pass furnace having an elongated firebox. The furnace 10 has end walls 12 and 14, side walls 16 and 18, top wall 20 and bottom wall 22. The walls are made of refractory material and define an elongated heating chamber 11 which has a horizontally disposed axis between ends 12 and 14. The width of the heating chamber 11 is about equal to its height and the heating chamber 11 has a substantially uniform cross section along its axis. At one end of the chamber there is provided a flue gas opening 24 through side wall 18. A duct 26 is arranged at the outlet end of the heating chamber 11. The duct 26 has an adjustable damper 28 for controlling the draft in the chamber. In operation, hot combustion gases from burners 36 discharge from the heating chamber 11 through the duct 26. The duct 26 is arranged at an angle to the axis of the chamber. It should be noted that the furnace of FIGS. 1 and 2 can be either vertically or horizontally disposed.

A metal tube conduit 30 carries a fluid stream in the heating chamber 11 from end wall 12 to end wall 14. Fittings, not shown, are provided for supplying the conduit 30 with fluid from feed line 32. The conduit 30 terminates at the end wall 14 and the fluid passes into a quench or discharge line 34. Again, suitable fittings, not shown, can be provided for connecting the conduit 30 with the discharge line 34. The feed and discharge lines are provided with valves for controlling the fluid stream passing through the conduit 30.

The conduit 30 is adapted to be heated by burners such as radiant type burners 36 which are disposed in the chamber in a straight or staggered row on each of side walls 16 and 18 substantially parallel with the axis of the conduit 30. As seen in FIGS. 1 and 2, each of the side walls 16 and 18 have six radiant type burners 36. The burners 36 are of the same type and capacity. A larger number of burners 36 are provided in the chamber half adjacent end wall 12 whereas a smaller number of such burners are provided in the chamber half near the end wall 14. Thus, the number of radiant burners 36 of substantially equal capacity is greater in the upstream area near the conduit inlet as compared to the downstream area near the conduit outlet. Alternatively, each of the burners can be equally spaced and fired differentially. The interior surfaces of the chamber walls, in cooperation with the burners, serve to emit intense radiant heat to the conduit 30. It will be understood that the chamber can have additional conduits passing therethrough, which can be parallel to conduit30.

The burners 36 are provided with suitable fuel by means of fuel lines 38, having adjustable valve means 40. .Each of the fuel lines 38 is connected directly to a manifold 42 into which fuel passes from lines 44. The fuel lines 44 are also provided with valve means 46 to regulate the passage of fuel therethrough. The burners 36 may be fired with either liquid or gaseous fuel, preferably gaseous fuel and conventional means can be provided for admixing the fuel with air in the burner.

In operation, the furnace is fired at a relatively intense rate near the fluid inlet and at a progressively less intense rate toward the downstream or outlet end. As a result of the design of the furnace, the hot combustion gases from the burners 36 flow toward the flue gas outlet 24, hence the flow of the combustion gases is cocurrently with the fluid in the conduit 30 from the furnace inlet to the furnace outlet.

Referring now to the embodiment of FIGS. 3, 4 and 5, the furnace of the present invention isshown arranged in a vertically disposed U-shaped furnace 50.The furnace 50 is comprised of a heating chamber 51 defined by U-shaped front wall 52, exterior side walls 54 which are connected at the furnace bottom by bottom bridging wall 56, U-shaped rear ,wall 58, top walls 66 and 68, partial partitionwalls 60 and'62 which are connected at one end by short bridging wall 64. The short bridging wall 64 is spaced from the bottom bridging wall 56 at about the same distance as the width of the chamber between wall 54and 60. With this structure, a centrally disposed opening 65 is provided between the partial partition walls 60 and 62.

The heating chamber 51 has a substantially uniform cross section throughout its length. The chamber is entirely closed within said walls except for a flue gas opening 24. As a consequence, all of the combustion gases must travel to the flue gas opening to discharge from the heating chamber 51.

Metal tube conduits 30 for carrying fluid are arranged in the furnace 50 to extend from the top wall 66 through the heating chamber 51 to the wall 68. Thus, the furnace inlet is at top wall 66 and the furnace outlet'is at top wall 68. A feed line 32 is arranged to pass through the top wall 66 and communicate with conduits 30 to supply feed therefor. The conduits 30 communicate at the discharge end with line 34 which passes through top wall 68. Line 34 leads to a quenching apparatus which is not shown. The conduits 30 are disposed in an offset relationship approximately equidistant from the opposed side walls in the heating chamber 51. The conduits 30 are disposed substantially parallel to the chamber axis throughout the entire length of the chamber. This necessitates a U-turn for the conduits adjacent bridging wall 56.

The furnace is tired by burners which may be either radiant or flame burners 72. In practice, it has been found that radiant burners 36 arranged on the side walls 54 and flame burners arranged on the partial partition walls 60 and 62 provide a suitable arrangement. Two rows of equally spaced radiant burners 36 are provided on each of the side walls 54. Each row has three radiant burners 36 on each wall for a total of six radiant type burners. The burners are arranged to extend through side wall 54. Directly opposite each of the radiant burners 36 is a pair of flat flame type burners 72. One of each pair of flat flame type burners 72 is mounted on the interior of the rear wall 52 and the companion burner to each pair is mounted on the front wall 58. The long flat flame burners uniformly heat the partition walls and side walls over relatively large areas and, provide heat combustion gases to flow cocurrently with the fluid in conduit 30. It should be noted that versatility inheres in this design of the furnace of the present invention. The arrangement, type and number of burners can vary. For example, alternative furnace embodiments can be fired by flat flame burners alone.

The burners 36 are provided with fuel by fuel lines 38, having valves 40. Each of the fuel lines 38 is connected to a manifold 42 which is fed fuelby a fuel line 44, also provided with a valve 46. With individual valves 40 for each fuel line 38, the individual burners 36 can be regulated selectively to afford accurate control of the furnace temperature profile.

In addition, the flat flame burners 72 are provided with fuel lines 90 which extend from a manifold 94 common to all the flat flame burners 72. Each fuel line 90 is provided with a valve 92 to regulate the flow of fuel to each flat flame burner 72. Similarly, the fuel line 98 feeding fuel to the manifold 94 is provided with a valve 100.

Any conventional thermostatic control devices can be used to vary the burner firing intensity as a function of the temperature of the fluid in conduit 30 or the temperature of the tube metal.

The furnace is provided with a flue gas outlet 70 which is located adjacent the outlet end of the fluid conduit 30. The opening 24 of the flue gas outlet 70 is at the top of the furnace just below the top wall 68. A damper 28, or similar means to control the furnace draft is also provided in the flue gas outlet 70. Consequently, by regulating the damper 28, the passage of hot combustion gases through the furnace can be controlled. An induced air fan 84 is also arranged in the flue gas outlet 70 to further facilitate control of the flow of the hot combustion gases through the furnace and flue gas outlet 70. It should also be noted that convection tubes or other waste heat recovery apparatus can be arranged in the flue gas outlet.

The furnace is supported on girders 74 which rest on legs 76 which, in turn, are supported by piles 78. Outwardly of the refractory chamber walls, there is intermediate block insulation 80 and outwardly of said insulation there is an outer shell 82,best seen in FIG. 3.

The present drawings do not show means for supporting or holding the conduits in position, however, various conventional means may be provided for supporting the conduits in the chamber. In the horizontal embodiment, a particularly suitable conduit support is shown in application Scr. No. 768,326 (Woebcke, filed Oct. 17, 1968). However, in the vertically disposed furnace embodiment, the tubes. would preferably be supported externally of the furnace by a conventional means, such as hangers.

In operation of the embodiment shown in FIGS. 3-5, a preheated fluid such as a normally liquid hydrocarbon feed admixed with steam enters the chamber through conduits 30 at end wall 66 and passes out of the conduits and the chamber at end wall 68. A relatively large heat flux obtains in the upstream area near the furnace inlet since the furnace feed is at its lowest temperature at the inlet. As the hot combustion gases travel downstream cocurrently with the fluid in the conduits 30 toward the flue gas opening 24, the downstream burners are fired at a lower rate. The heat flux progressively diminishes as the fluid flows downstream since the temperature difference between the fluid in the conduits 30 and the temperature of the heating chamber is decreased.

Consequently, the fluid in conduits 30 and the hot combustion gases emanating from the furnace burners travel a cocurrent path through the furnace until both exit at effectively the same location. Therefore, the transfer of heat from the hot combustion gases is continuous from the point of initial contact until the combustion gases exhaust from the furnace. The coincident travel and continuous heat exchange of the fluid in the conduit and the hot combustion gases causes the fluid .to increase in temperature while the temperature of the hot gases decreases, thereby approaching an ideal furnace condition. Therefore, it is inherent in the design of the furnace of the present invention that a temperature profile exist. Thus, the maintenance of a constant tube metal temperature at all points on the conduit 30 is facilitated by the basic furnace design.

In addition, the presence of valve means to regulate the fuel input to each burner and means to regulate the draft in the flue gas outlet affords means to accurately control the temperature profile of the furnace. By selective regulation of the valves 40 and 92 in the fuel lines 38 and 90, the heat flux can be controlled at localized areas along the conduits 30. Conversely, by regulating the damper 28, the furnace draft can be varied to thereby increase or decrease the length of time the hot combustion gases are maintained in heat exchange relationship with the fluid in the conduits 30.

The process as it relates to this embodiment is further described and compared with that of a conventional furnace in the Example, Table I and in FIGS. 6 and 7. FIG. 6 shows the temperature profile of the conventional furnace (Furnace A of Table l) whereas FIG. 7 shows a profile for a furnace. (F urnace B of Table I), of this invention when such furnaces are operated under the conditions shown in Table I. In both FIGS. 6 and 7 the metal tubes are of 2 inch internal diameter, 2.5 inches outside the diameter, and 90 feet long.

EXAMPLE The following Example and the comparison of Tables 1 and 2 indicate the versatility of the furnace of the present invention. Table I will illustrate the furnace of the present invention affording lower operating tube metal temperature while Table 2 illustrates the present invention affording shorter tube length and increased ethylene yield.

Table l below gives a comparison of the relative parameters for two furnaces. Furnace A consists ofa close looped coil in a conventional single cell firebox. Furnace B consists of a coil, the same length and diameter of tube as in Furnace A but disposed and fired according to this invention and particularly in accordance with the embodiment of FIGS. 3-5. In both Furnace A and Furnace B, the metal tube conduits are of2 inches internal diameter, 2.5 inches outside diameter and 90 feet long. The flow of fluid through the tubes for each of the furnaces, in pounds per hour, is 1,150 for the hydrocarbon and 575 for steam for a total flow of 1,725 (pounds per hour). Furnaces A and B are designed to have the same coil inlet and outlet temperature.

From the above Table I, it can be seen that for the same coil outlet temperature and essentially the same residence time, Furnace B has an efficiency of 48.7 percent as opposed to 42.6 percent for Furnace A. This increase in efficiency would result in a 14.2 percent saving of fuel fired. Furthermore, for substantially the same heat input to the coil, the maximum tube metal temperature is 92 F. lower in Furnace B than in Furnace A.

Conversely, the furnace of the present invention can be designed to afford increased ethylene yield by operating at the maximum presently allowable tube metal temperature. Again, Furnace A is the conventional close looped coil, single cell firebox. Furnace C is a furnace disposed and fired in accordance with the furnace embodiment of FIGS. 3-5, but designed to operate at the maximum presently allowable tube metal temperature. With this design, it can be see that the length of the tubes of Furnace C is less than the length of Furnace A, the residence time is less and the ethylene yield is greater.

The present invention has been described with reference to a specific apparatus and process. It should be noted that the invention is not limited to the specific apparatus and process, but extends to the various embodiments comprehended in the invention as claimed.

As a consequence of the basic furnace design of the present invention, maximum heat exchange between the hot combustion gases and the fluid in the furnace conduit is afforded. With the hot combustion gases and the fluid in the conduit flowing parallel and cocurrently, they are effectively maintained in heat exchange relationship during their entire passage through the furnace. Therefore, the furnace of the present invention affords the further advantage of refined heat flux control.

Heat flux is a measure of heat exchange in that it is the number of BTUs/hr./sq. ft. that the fluid passing through the conduit will absorb from the heat energy generated by the furnace burners. Therefore, as a general rule, the greater the temperature difference between the burner combustion gases and the fluid in the furnace conduit, the greater the heat flux. Consequently, in the furnace of the present invention, the heat flux in the upstream area near the furnace inlet is substantially greater than in the downstream area. The hot combustion gases in the chamber are continually being cooled as they transfer heat to the fluid in the conduit. Hence it is possible to maintain a substantial temperature gradient along the length of the firebox. By placing burners along the entire length of the furnace heating chamber, it is possible to maintain the maximum safe conduit temperature while still maintaining strength of the conduit material along the whole length of the conduit. Thus, optimum heat input to the conduit for a given maximum safe conduit material temperature is achieved. Also, by placing burners along the entire length of the furnace heating chamber, the temperature gradient can be changed at desired points along the length of the conduit.

This invention includes means for controlling the radiant heat input to the conduit from burners along the entire length of the coil. Such control can be attained by the relative number, type, or heating capacity, or simply adjustment of the burners or combinations of such specific means. However, the burners can all be in the upstream area and the downstream area and can be heated simply from the hot burner combustion gases. In one embodiment wherein the same number and capacity of burners are in both the upstream and downstream areas, the burners in the upstream area can be fired at high rates to produce a highrate of heat-transfer per unit of area per unit of time while burners in the downstream area can be fired at a much lower rate to produce a much lower rate of heat transfer. In still another embodiment, the burners are of the same type and capacity and are adjusted to the same rate of heat transfer, but a greater number of such burners are in the upstream area as compared to the downstream area.

The process of the present invention can be carried out to obtain selective chemical conversions of specific hydrocarbons. The hydrocarbon feed can be.in the liquid or vapor phase or mixed liquid-vapor phase. The hydrocarbon feed can be diluted with steam at a weight ratio such as that of about 0.1 to 2 and preferably 0.3 to l. The hydrocarbon is normally in vapor phase in the reaction zone. The feed will generally be preheated in the preheat zone from about ambient temperature, e.g. 70 to 80 F. to a temperature below that at which significant reaction takes place, e.g. 1,100 to l,200 F. During the preheat step, depending on the boiling range of the feed, the feed may be partially or completely vaporized. In the process where steam is used, steam is added to the feed prior to the feed being introduced to the reaction zone. For example, the steam can be added at points in the preheat section at which the feed is 70 to 90 percent vaporized. The steam, when added in this manner, acts to completely vaporize the feed by reducing the hydrocarbon partial pressure in the reaction zone; i.e., in the furnace chamber.

The inlet temperature of the fluid into the furnace of this invention will be about 1,100" to 1,200 F. and the outlet temperature adjacent to the flue gas passageway will be about l,500 to l,650 F. The feed rate is such that the mass velocity of the feed through the furnace conduit or conduits can be to 35 pounds per. second, per square foot, of cross sectional area, preferably, 18 to 26 pounds per second, per square foot. The mass velocity when steam is used is based on the total flow of steam and hydrocarbons.

The residence time of the feed in the furnace of this invention can be 0.10 to 0.50 second and preferably, 0.15 to 0.40 second. At the high temperatures used, the cracking reactions take place very rapidly. in order to prevent production of large amounts of undesirable by-products and in order to prevent severe coke deposition, it is necessary to cool rapidly the effluent product gases from the furnace exit temperature of l,500 to l,700 F. to a temperature at which the cracking reactions substantially stop. On leaving the furnace, the feed is subjected to quenching in order to arrest any additional chemical reaction. The quenching can be carried out by conventional equipment and procedures.

The average heat flux provided by the burners in the upstream area will vary from about 20,000 to 40,000 BTU/hr./sq. ft. The average heat flux in the downstream area will be lower than this, e.g. below 20,000 BTU/hr./sq.ft. The conduit can have inlet fluid pressure at the furnace chamber of 30 to 75 PSlA and an outlet pressure of 20 to 45 PSlA as it leaves the chamber. The conduit can be from about 60 to 210 feet in length within the furnace chamber with inside conduit diameters of about 2 to 3 inches.

The specific operating conditions of the furnace of this invention are dependent on the characteristics of the feed stock and the desired products. The length of the furnace, the length of the conduits and their inside diameter, are selected to provide the desired residence time.

Advantages of this invention include: (a) maintaining the whole length of the conduit material, preferably a metal tube, at substantially the same temperature which results in the maximum heat input to the conduit for a specific conduit material temperature; (b) easily changing the temperature profile of the combustion gases throughout the entire length of the furnace giving great flexibility in controlling the temperature profile of the fluid within the conduit which results in improved product yields or distribution; and (c) since the hot combustion gases leave the furnace at a temperature which is substantially lower than the average firebox temperature, a very substantial improvement in furnace efficiency is obtained.

What is claimed is:

1. Apparatus for the continuous heat treatment of a fluid comprising:

a furnace heating chamber;

a chamber inlet end;

a chamber outlet end;

a conduit arranged to extend from the chamber inlet to the chamber outlet and disposed parallel to the axis of the chamber, said conduit adapted to carry fluid from the chamber inlet to the chamber outlet;

a flue gas opening disposed at the chamber outlet end; and

burners located in the furnace heating chamber in proximity to the chamber inlet end for providing the furnace heating chamber with hot combustion gases, said hot combustion gases adapted to flow substantially parallel and cocurrently with the flow of fluid in the conduit.

2. Apparatus as in claim 1 further comprising means to regulate the draft in the flue gas opening.

3. Apparatus as in claim 2 further comprising valves in the fuel lines to the burners to regulate the burners and wherein the means to regulate the draft in the flue gas opening is a damper.

4. Apparatus as in claim 3 wherein the axis of said chamber is vertically disposed and the flue gas opening is at an angle from the chamber axis.

5. Apparatus as in claim 1 wherein the burners are long flat flame burners.

6. Apparatus for the continuous heat treatment of a fluid comprising:

a vertically disposed furnace heating chamber;

a chamber inlet end;

a chamber outlet end;

a conduit arranged to extend from the chamber inlet to the chamber outlet and disposed parallel to the axis of the chamber, said conduit adapted to carry fluid from the chamber inlet to the chamber outlet;

a flue gas opening disposed at the chamber outlet end at an angle to the chamber axis;

two rows of radiant burners arranged on one side wall and two rows of long flat flame burners on the side wall opposite the wall having the radiant burners located in the furnace heating chamber in proximity to the chamber inlet end for providing the, furnace heating chamber with hot combustion. gases, said hot combustion gases adapted to flow substantially parallel and cocurrently with the flow offluid in the conduit;

valves in the fuel lines to the burners to regulate the burners; and

a damper in the flue gas opening to regulate the draft therein.

7. A furnace for the continuous heat treatment of a fluid comprising:

vertically disposed U-shaped elongated heating chamber;

a flue gas passageway at one end of the elongated chamber, said passageway disposed laterally of the chamber end;

radiant heating burners in one side wall of the upstream area of the heating chamber;

long flat flame burners in the side wall opposite the wall having the radiant burners;

a conduit for the fluid to be heated, said conduit disposed parallel to the axis of the chamber substantially throughout the length thereof to an outlet adjacent to the flue gas passageway;

means for controlling heat flux in the primary heating zone and in the second half of the chamber, said means providing greater heat flux in the primary zone as compared to the second half of the chamber; and

means to regulate the flow through the flue gas passageway;

whereby the hot combustion gases flow substantially parallel to the conduit in the direction of the flow of fluid from the burners to the flue gas passageway.

8. A process for heating a fluid comprising the steps of:

passing the fluid in a continuous stream through a metal conduit disposed in an elongated chamber having a flue gas passageway adjacent the conduit stream outlet end of said chamber;

subjecting a first portion of said conduit adjacent the stream inlet end to heat from burners, said burners emitting hot combustion gases;

conducting the heated combustion gases from said burners through the chamber toward the flue gas opening substantially parallel and cocurrently with the flow of fluid in said conduit; and

heating the fluid in the conduit beyond the first portion by both burners and by the heated combustion gases, said combustion gases cooling while transferring heat to said conduit, and regulating the heat transferred to said conduit and fluid to provide greater heat flux thereto in the first longitudinal portion as compared to the heat flux provided to the conduit beyond said portion, wherein the temperature of the metal conduit is maintained within a 5 percent variation from substantially one end thereof to the other in said chamber and wherein the heat flux in said chamber is controlled to raise the temperature of the fluid in the conduit from the inlet to the outlet end while the temperature of combustion gases flowing substantially parallel and cocurrently with the fluid is lower at the outlet end as connected to the inlet end. 

1. Apparatus for the continuous heat treatment of a fluid comprising: a furnace heating chamber; a chamber inlet end; a chamber outlet end; a conduit arranged to extend from the chamber inlet to the chamber outlet and disposed parallel to the axis of the chamber, said conduit adapted to carry fluid from the chamber inlet to the chamber outlet; a flue gas opening disposed at the chamber outlet end; and burners located in the furnace heating chamber in proximity to the chamber inlet end for providing the furnace heating chamber with hot combustion gases, said hot combustion gases adapted to flow substantially parallel and cocurrently with the flow of fluid in the conduit.
 2. Apparatus as in claim 1 further comprising means to regulate the draft in the flue gas opening.
 3. Apparatus as in claim 2 further comprising valves in the fuel lines to the burners to regulate the burners and wherein the means to regulate the draft in the flue gas opening is a damper.
 4. Apparatus as in claim 3 wherein the axis of said chamber is vertically disposed and the flue gas opening is at an angle from the chamber axis.
 5. Apparatus as in claim 1 wherein the burners are long flat flame burners.
 6. Apparatus for the continuous heat treatment of a fluid comprising: a vertically disposed furnace heating chamber; a chamber inlet end; a chamber outlet end; a conduit arranged to extend from the chamber inlet to the chamber outlet and disposed parallel to the axis of the chamber, said conduit adapted to carry fluid from the chamber inlet to the chamber outlet; a flue gas opening disposed at the chamber outlet end at an angle to the chamber axis; two rows of radiant Burners arranged on one side wall and two rows of long flat flame burners on the side wall opposite the wall having the radiant burners located in the furnace heating chamber in proximity to the chamber inlet end for providing the furnace heating chamber with hot combustion gases, said hot combustion gases adapted to flow substantially parallel and cocurrently with the flow of fluid in the conduit; valves in the fuel lines to the burners to regulate the burners; and a damper in the flue gas opening to regulate the draft therein.
 7. A furnace for the continuous heat treatment of a fluid comprising: vertically disposed U-shaped elongated heating chamber; a flue gas passageway at one end of the elongated chamber, said passageway disposed laterally of the chamber end; radiant heating burners in one side wall of the upstream area of the heating chamber; long flat flame burners in the side wall opposite the wall having the radiant burners; a conduit for the fluid to be heated, said conduit disposed parallel to the axis of the chamber substantially throughout the length thereof to an outlet adjacent to the flue gas passageway; means for controlling heat flux in the primary heating zone and in the second half of the chamber, said means providing greater heat flux in the primary zone as compared to the second half of the chamber; and means to regulate the flow through the flue gas passageway; whereby the hot combustion gases flow substantially parallel to the conduit in the direction of the flow of fluid from the burners to the flue gas passageway.
 8. A process for heating a fluid comprising the steps of: passing the fluid in a continuous stream through a metal conduit disposed in an elongated chamber having a flue gas passageway adjacent the conduit stream outlet end of said chamber; subjecting a first portion of said conduit adjacent the stream inlet end to heat from burners, said burners emitting hot combustion gases; conducting the heated combustion gases from said burners through the chamber toward the flue gas opening substantially parallel and cocurrently with the flow of fluid in said conduit; and heating the fluid in the conduit beyond the first portion by both burners and by the heated combustion gases, said combustion gases cooling while transferring heat to said conduit, and regulating the heat transferred to said conduit and fluid to provide greater heat flux thereto in the first longitudinal portion as compared to the heat flux provided to the conduit beyond said portion, wherein the temperature of the metal conduit is maintained within a 5 percent variation from substantially one end thereof to the other in said chamber and wherein the heat flux in said chamber is controlled to raise the temperature of the fluid in the conduit from the inlet to the outlet end while the temperature of combustion gases flowing substantially parallel and cocurrently with the fluid is lower at the outlet end as connected to the inlet end. 